Atomic force microscopy study of the structural effects induced by echinomycin binding to DNA

Area of Science:

• Molecular Biology
• Biophysics

Background:

• Echinomycin is a DNA bis-intercalating antibiotic.
• Understanding its interaction with DNA is crucial for drug development and DNA structural studies.

Purpose of the Study:

• To investigate the conformational effects of echinomycin on linear and circular DNA using atomic force microscopy (AFM).
• To analyze the impact of modified DNA bases on echinomycin binding and DNA structure.
• To quantify structural changes in plasmid DNA upon echinomycin binding.

Main Methods:

• Synthesis of four different 398 bp DNA fragments with normal and modified bases (2,6-diaminopurine and inosine).
• Atomic force microscopy (AFM) to measure DNA contour lengths and assess bis-intercalation.
• Determination of dissociation constants to evaluate binding affinities.
• Investigation of structural perturbations in closed circular pBR322 DNA using AFM.

Main Results:

• Echinomycin bis-intercalation was quantified, with approximately 66 molecules binding per fragment, indicating a site size of six base-pairs.
• Modified nucleotides significantly affected DNA conformation, altering the helical rise per base-pair.
• Dissociation constants revealed preferential binding of echinomycin to TpA sites over CpG sites.
• Increasing echinomycin concentration induced transitions in plasmid DNA supercoiling: decrease, relaxation, and subsequent increase.

Conclusions:

• The study quantifies echinomycin binding to DNA and demonstrates the influence of modified bases on DNA conformation and drug interaction.
• Echinomycin exhibits sequence-specific binding preferences, impacting DNA structural dynamics.
• AFM provides a valuable method for visualizing and quantifying drug-induced DNA structural changes, including alterations in supercoiling.